PSEB Solutions for Class 10 Science Chapter 13 Magnetic Effects of Electric Current

PSEB Solutions for Class 10 Science Chapter 13 Magnetic Effects of Electric Current

PSEB 10th Class Science Chapter 13 Magnetic Effects of Electric Current

→ A current-carrying conductor behaves like a magnet. Magnet and electricity are related to each other.

→ Hans Christian Oersted did remarkable work to make us understand electromagnetism.

→ That end of freely suspended magnet which points towards north direction is called North Seeking or the North Pole and the other end which points towards south direction is called South Seeking or the South Pole.

→ Like poles repel each other while unlike poles attract each other.

→ The field or area around a magnet in which its effect or force can be experienced is called the magnetic field of the magnet.

→ The direction of magnetic lines of force inside the magnet is from the south pole to the north pole while outside the magnet it is from the north pole to the south pole. Therefore, magnetic lines are closed curves.

→ Two magnetic lines of force never intersect each other.

→ On passing a current through a metallic conductor, the magnetic field is produced around it.

→ The magnetic field produced all around it is inversely proportional to its distance.

→ The magnetic field at a point inside the magnetic field produced due to the current flowing through a conductor is proportional to the current flowing through the conductor.

→ A coil consisting of a cylindrical-shaped coil having closely packed turns of insulated copper wire is called a solenoid.

→ Inside a solenoid, magnetic lines of force are just like parallel straight lines. The magnetic field is the same at all points inside the solenoid.

→ The force acting in a conductor is in the direction of current and perpendicular to the direction of the magnetic field. This is called Fleming’s left-hand rule.

→ Electric motor, electric generator, loudspeaker, microphone, and electric meter are related with current-carrying conductor and magnetic field.

→ Production of the magnetic fields is necessary for our heart and brain.

→ MRI is important in medical treatment.

→ The electric motor is a device in which electrical energy is transformed into mechanical energy.

→ Electric motors find their use in electric fans, refrigerators, electric mixers, washing machines, computers, MP3 players, etc.

→ In electric motors, a rectangular coil of insulated wire is placed in between two poles.

→ That device that alternately changes the flow of current is called an AC motor.

→ Soft iron core and coil together form an armature. This increases the power of the motor.

→ Faraday discovered how the moving magnet can be used in producing current.

→ A galvanometer is an instrument that is used to detect the presence of current in a circuit.

→ That process by which the change in the magnetic field of a conductor produces a current in another conductor is called electromagnetic induction.

→ When the direction of motion of a coil is perpendicular to the direction of the magnetic field, then the induced electric current in the coil becomes maximum.

→ In electric generators, mechanical energy is used to rotate a conductor placed in a magnetic field as a result of which current is produced.

→ The device used to produce electricity is called an A.C. generator.

→ Electromagnet: A soft iron piece placed inside an insulated conducting coil becomes an electromagnet on passing current.

→ Magnetic Field: The field around a magnet in which its effect can be felt.

→ Solenoid: A coil made by winding a conducting wire having a large number of closed turns.

→ Iron Core: The soft iron rod placed inside the solenoid is called the iron core.

→ Snow Rule: When a wire placed above a magnetic needle carries current from the south direction to the north direction then the north pole (N-pole) of the magnetic needle gets deflected westward.

→ Electromagnetic Induction: Due to change in the magnetic field the current produced in the neighboring coil is called electromagnetic induction.

→ Electric Energy: The capacity for doing work by an electric current is known as electric energy.

→ Electric Power: The rate at which electric energy is consumed in a conductor is called electric power.

→ Electric Generator: The instrument which produces electric current is called an electric generator.

→ Alternating Current (A.C): That current which continuously changes direction alternately is called alternating current.

→ Direct Current (D.C.): That current which has the same direction always is called direct current (D.C.)

→ Short Circuit: When the live wire comes in direct contact with the neutral wire due to damaged wiring or uncovered wire, the resistance of the circuit becomes zero, and the current flowing through the circuit increases suddenly. This is called short-circuiting.

→ Fuse (Safety Fuse): A wire of low melting point connected in an electric circuit is called a fuse.

→ Electric Meter: A device that is connected to an electric circuit to measure electric energy being used is called an electric meter.

→ Electric Shock: When any part of the human body touches any point of the unsheathed (without insulation) circuit having high potential, shock is experienced which is known as electric shock.

→ Overloading: If the current through a circuit is more than the maximum prescribed limit then the wires become hot and may catch fire. It is called overloading.

→ Right Hand Thumb Rule: If we imagine that current is passing through a conductor held in your right hand such that the thumb points in the direction of current then the curling fingers would represent the direction of the magnetic field.

→ Flemming’s Left-Hand Rule: Stretch your left hand in such a way that the first central fingers are mutually perpendicular to each other, then if the first finger points in the direction of the magnetic field, the central finger in the direction of current then the thumb points in the direction of motion of the conductor.

→ Earthing: The joining of metallic frame of the electric appliance of high power with the earth wire of domestic circuit is called earthing.

Science Guide for Class 10 PSEB Magnetic Effects of Electric Current InText Questions and Answers

Question 1. Why does a compass needle get deflected when brought near a bar magnet?
Answer:
A compass needle is a small bar magnet with one end as north and the other end as south pole. It is a well known fact that similar poles repel each other and dissimilar poles attract each other. When N-pole of a bar magnet is brought near the compass, the north pole of compass gets repelled while its S-pole is attracted so that compass needle gets deflected.

Question 2. Draw magnetic lines around a bar magnet.
Answer:
Place a bar magnet in the middle of a sheet of paper fixed on drawing board by using adhesive tape. Mark the boundary of the magnet with pencil. Place compass near north pole of the magnet when south pole of the compass will point towards north pole of the magnet. Mark the two points a, b at the two ends of the needle. Move the needle to a new position such that S-pole of compass needle is at b [position previously held by N-pole].

Repeat this till you reach south pole of the magnet (Figure).

Drawing magnetic field lines by compass needle.

Now Join the marked points on a paper by a smooth line which gives one magnetic line of force as shown in Figure. Repeat this procedure taking Figure Magnetic field around a bar different starting points.

Magnetic field around a bar magnet.

Question 3. List the properties of magnetic lines of force.
                         Or
Write characteristics of magnetic field lines.
Answer:
Properties (characteristics) of magnetic lines of force are :

• These are the closed curves passing through the magnet. Outside the magnet lines of force start from north pole of the magnet and end at the south pole and inside the magnet, the direction of magnetic lines are from south pole to north pole.
• The two magnetic lines of force never intersect each other.
• They have a tendency to contract lengthwise which explains the attraction between opposite poles.
• The tangent at any point of the magnetic lines of force gives the direction of the field at that point.
• They exert lateral pressure upon each other, which explains repulsion between like poles.

Question 4. Why two magnetic lines of forces never intersect each other?
Answer:
No two magnetic lines of force cross each other because, if they did so, then at the point of intersection; the compass needle would point towards two directions at the same time, which is not possible. Hence two magnetic lines never intersect each other.

Question 5. Consider a circular loop of wire lying in the plane of the table. Let the current pass through the loop clockwise. Apply right hand rule to find out the direction of the magnetic field inside and outside the loop.
Answer:
The direction of the magnetic field inside and outside loop is as shown in Figure. By applying right hand rule we find that the direction of magnetic field inside the loop is downward normally and outside the loop it is normal to the plane of paper.

Question 6. The magnetic field in a given region is uniform. Draw a diagram to represent it.
Answer:
Uniform magnetic field is shown by equidistant and parallel lines as shown in Figure If the parallel lines are close to each other, the field is strong. The stronger the field, the closer are the lines.

Question 7. Choose the correct option.
The magnetic field inside a long straight solenoid carrying current (a) is zero ;
(b) decreases as we move towards end ;
(c) increases as we move towards end;
(d) is same at all the points.
Answer:
(d) is correct. The magnetic field inside a long straight solenoid is same at all the points.

Question 8. Which of the following property of proton can change while it moves freely in a magnetic field? [There may be more than one correct answer].

(a) mass
(b) speed
(c) velocity
(d) momentum.
Answer:
(c) Velocity and (d) Momentum.

Question 9. In activity shown, how do you think the displacement of rod AB will be affected :
(i) if the current in rod AB is increased;
Answer:
Since force acting on the rod is directly proportional to the current passing through it. Therefore, the displacement will be increased when current is increased.

(ii) a stronger horse shoe magnet is used;
Answer:
Stronger the magnet, more will be the force and hence the displacement.

(iii) length of the rod AB is increased.
Answer:
Force is also directly proportional to the length of the rod. Hence rod will be displaced more if the length is increased.

Question 10. A positively charged particle emitted from a nucleus alpha particle projected towards west is deflected towards north by a magnetic field. The direction of the magnetic field is :
(a) towards south
(b) towards east
(c) downward
(d) upward.
Answer:
(d) upward [In accordance with Fleming’s left hand rule]

Question 11. State Fleming’s left hand rule.
Answer:
Fleming’s left hand rule. It states, “Stretch the thumb, fore finger and middle finger of your left hand such that they are mutually perpendicular to each other. If the first finger points in the direction of magnetic field and central (second) finger points towards the direction of current then thumb points towards the direction of motion as shown in Figure.

Flemmgs left hand rule for direction of force on current carrying conductor

Question 12. What is the principle of an electric motor?
Answer:
Principle of Electric motor. Electric motor is based upon the principle that when a current carrying coil is placed in a uniform magnetic field, it experiences torque which rotates the coil.

Question 13. What is the role of the split ring in an electric motor?
Answer:
The split rings act as a commutator in D.C. motor i.e., it reverses the direction of current through the circuit after every half cycle.

Question 14. Explain different ways to induce current in a coil.
Answer:
There are mainly two methods to induce current in a coil.

Induced current due to relative motion between coil and magnet.

When the magnet is stationary [at rest as in Figure (a)], no induced current is produced.
1. When magnet is moving with its N-pole towards the coil, deflection in galvanometer is as shown in Figure (b). Direction of the current gets reversed when N-pole is withdrawn from inside the coil (going away from coil) as shown in Figure (c). Faster the magnet moves, more is the deflection and hence current in galvanometer.

Deflection produced in the galvanometer needle by the current is same when N-pole was moving down [Figure (6)] or when south pole is out of the coil [Figure (e)].

Current and hence deflection in the galvanometer needle will be again produced if magnet is kept at rest and coil is moved.

2. By changing current in the neighbouring circuit. Take a non¬conducting cylindrical tube (say of card board). Wind two set of coils I and. II on it as shown. Connect a battery and a key to the ends of coil I and a galvanometer to the ends of coil II. When plug is inserted in key K, there will be an instantaneous deflection m galvanometer even though there is no cell in this circuit. Now take out the plug from key K. An instantaneous large deflection in opposite direction to previous deflection will be produced in galvanometer. Thus current has been induced in coil II due to increase or decrease of current in coil I.

Induced Current by changing current m the neighbouring circuit.

Question 15. State the principle of electric generator.
Answer:
Principle of Electric Gen¬erator. Electric generator is based upon Fleming’s right hand rule.

Right hand rule

Fleming’s right hand rule. Stretch the thumb, fore-finger, control (middle) finger of right hand so that they are perpendicular to each other. If fore-finger indicates the direction of magnetic field, the thumb shows the direction of motion of the conductor, the central (middle) finger will show the direction of induced current.

Question 16. Name some sources of direct current.
Answer:
Sources of direct current are

• Cell
• Battery
• D.C. generator.

Question 17. Which sources produce alternating current?
Answer:
Alternating current is produced by A.C. generators. There are hydro-generator and thermal generators.

Question 18. Choose the correct option :
A rectangular coil of copper wires is rotated in magnetic field. The direction of induced current changes once in each:
(a) two revolutions
(b) one revolution
(c) half revolution
(d) one-fourth revolution.
Answer:
(c) half rotation.

Question 19. Name two safety measures commonly used in electric circuits and appliances.
                                             Or
Write the two safety measures commonly used in electric circuit appliances.
Answer:
Common Safety Measures used in Electric Circuits. Two most common safety measures used, are :

• A safety fuse of proper rating connected in a circuit prevents damage to the electric appliances and also the circuit due to overloading or short circuiting.
• Earth wire prevents possible electric shock when live wire incidently touches the body of appliance.

Question 20. An electric oven of 2kW power rating is operated in a domestic electric circuit (220 V) that has a current rating of 5 A. What result do you expect? Explain.
Answer:
Given : Power of oven (P) = 2 kW
= 2,000 W
Voltage (V) =220 volts
Current (I) =?

We know that, P = V x I
or I = P/V
Current (I) = 2,000/200
= 100/11
= 9.09 A

A current of 9.09 A will flow in the circuit. Since the current rating of circuit is 5 A, the fuse (of 5 A) rating if inserted in the circuit will burn up. If no fuse is placed in the circuit, there may be a fire.

Question 21. What precautions should be taken to avoid the overloading of domestic electric circuits?
Answer:
Precautions to avoid overloading.

• Wires used for carrying current should be of proper current rating. Whereas wire of low current rating may be used for lighting electric bulbs, tubes, T.V. etc., and wires of higher current rating should be used for A.C., heating appliances etc.
• There should be a separate circuit for heating appliance.
• PVC of good quality should be used for insulating wires.
• Each circuit should have a fuse of proper rating.
• After every 3-4 years wires should be replaced by new wires of proper rating.

PSEB 10th Class Science Guide Magnetic Effects of Electric Current Textbook Questions and Answers

Question 1. Which of the following correctly describes the magnetic field near a long wire? The field consists of :
(a) straight lines perpendicular to the wire.
(b) straight lines parallel to the wire.
(c) radial lines originating from the wire.
(d) concentric circle centred on the ware.

Answer:
(d) concentric circles centred on the wire (Figure)

Question 2. The phenomenon of electromagnetic induction is :
(а) the process of charging a body.
(b) the process of generating magnetic field due to a current passing through a coil.
(c) producing induced current in a coil due to relative motion between a magnet and the coil.
(d) the process of rotating the coil of an electric motor.
Answer:
(c) producing induced current in a coil due to relative motion between a magnet and the coil.

Question 3. The device used for producing electric current is called :
(a) generator
(b) galvanometer
(c) ammeter
(d) motor.
Answer:
(a) generator.

Question 4. The essential difference between an AC generator and a DC generator is that:
(а) AC generator has an electromagnet while a DC generator has a permanent magnet.
(б) DC generator will generate higher voltage.
(c) AC generator will generate higher voltage.
(d) AC generator has slip rings while the DC generator has a commutator.
Answer:
(d) AC generator has slip rings while DC generator has a commutator.

Question 5. At the time of short circuit, the current in the circuit.
(a) reduces substantially
(b) does not change
(c) increases heavily
(d) vary continuously.
Answer:
(c) increases heavily.

Question 6. State whether the following statements are true or false.
(a) An electric motor converts mechanical energy into electric energy.
(b) An electric generator works on the principle of electromagnetic induction.
(c) The field at the centre of a long circular coil carrying current will be parallel straight lines.
(d) A wire with a green insulation is usually the live wire.
Answer:
(a) is false. It converts electric energy to mechanical energy.
(b) is true.
(c) is true.
(d) is false. Green is usually earth wire.

Question 7. List three sources of magnetic field.
Answer:
Sources of Magnetic field are :

• Magnet.
• Current carrying conductor
• Current carrying solenoid.

Question 8. How does a solenoid behave like a magnet? Can you determine north and south poles of current carrying solenoid with the help of bar magnet? Explain.
Answer:
Solenoid: It consists of a coil of a number of turns of insulated copper wire closely wound in the shape of a cylinder. Magnetic field around a current carrying solenoid is shown in Figure.

Field lines of the magnetic field inside and around a current carrying solenoid.

These magnetic lines due to current carrying solenoid appear to be similar to that of a bar magnet shown in Figure.

One end [right end] of solenoid behaves like north pole and the other end [left end] behaves like south pole. Magnetic field lines inside the solenoid are in the form of parallel straight lines. This means that the field is the same at all points inside the solenoid.

Field lines around a bar magnet.

A soft iron rod when placed inside the solenoid behaves, like an electromagnet.

Question 9. When is, the force experienced in a magnetic field, the largest?
Answer:
When the field is perpendicular to current carrying conductor, the force experienced by a current carrying conductor placed in a magnetic field is largest.

Question 10. Imagine that you are sitting in a chamber with your back to one wall. An electron beam moving horizontally with back towards the front wall, is deflected by a strong magnetic field to your right side. What is the direction of the magnetic field?
Answer:
The magnetic field will be acting in vertically downward direction in accordance with Fleming’s left hand rule. [Direction of the current should be considered in a direction opposite to the direction in which the electrons move].

Question 11. Draw a labelled diagram of an electric motor. Explain its principle and working. What is the function of a split ring in electric motor?
Answer:
Electric motor: It is a device which is used to convert electric energy into mechanical energy.
Principle, “When a current carrying coil is placed in a uniform magnetic field, it experiences a torque which rotates the coil.”

I indicates direction of current; F the direction field and M the direction of motion

Working: A direct current from a battery is passed through armature. The current flows in the coil along ABCD as shown in Figure (a). The limb AB of the coil experience downward and CD of the coil experience upward force in accordance with Fleming’s left hand rule. These two equal and opposite forces constitute a couple tending to rotate the coil in clockwise direction. After half the rotation, brush B₁ has contact with S₂ and brush B₂ with S₁. The direction of the current gets reversed. The current now flows along DCBA instead of along ABCD. Limb DC experiences downward and BA experiences an upward force in accordance with Fleming’s left-hand rule.

The process repeats itself and motion of armature becomes continuous after some time.
Functions of Split rings. They help in reversing the direction of current in the coil after every half rotation.

Question 12. Name some devices in which electric motors are used.
Answer:
Electric motor are used in battery operated toys, in tape recorder, in car fans, mixers, grinders, computers and variety of other electric appliances.

Question 13. A coil of insulated copper wire is connected to a galvanometer. What will happen if a bar magnet is (i) pushed into the coil; (ii) withdrawn from inside the coil; (iii) held stationary in the coil?
Answer:

• When the bar is pushed into the coil, there will be momentary deflection of galvanometer in one direction. This is so because when magnet is brought near the coil, magnetic lines linked with the coil increases, so that induced emf is produced which induces current in the coil.
• Faster, we push the magnet, more will be the deflection.
• When the bar magnet is withdrawn, there will again be momentary galvanometer deflection but in a direction opposite to that when magnet was pushed in. This time also current is induced in the coil.
• When the magnet is held stationary inside the coil, there will be no deflection in galvanometer. It is because no emf is induced and hence no current is induced in the coil.

Question 14. Two circular coils A and B placed closed to each other. If the current in the coil A is changed, will some current be induced in coil B? Give reason.
Answer:
If the current in the coil is changed (switched on or switched off), then an electric current is induced in coil B. ‘

It is because when, plug in the key is introduced, current flows through the coil ‘A’ so that magnetic field is produced all round it. These magnetic lines produced in the coil ‘A’ will pass through the coil ‘B’ with the result induced emf and hence induced current is produced in the coil ‘B’ which is indicated by deflection of the galvanometer. Now when plug is removed from the key (switched off) the magnetic lines of force Jinked with the coil ‘B’ again change (decreases). This time again current is induced in the coil ‘B’.

Question 15. When does an electric short circuit occur?
Answer:
Electric short-circuit occurs when :

• live wire incidently touches neutral or earth-wire.
• insulation around the current carrying wires is weak.
• insulation gets hardened by the excessive use.
• current passed through wire is more than its rating.

Question 16. What is the function of earth wire? Why is it necessary to earth metallic appliances?
Answer:
Earth wire. It is used as a safety measure especially for electric appliance having metallic body. The metallic body of appliances like electric press, fans, toasters, refrigerators etc. are connected to earth wire which provides an easy path for current to go to the earth in case live wire touches the body of appliance incidently. The user will not suffer a severe electric shock in the event of touching a defective appliance.

Question 17. State two properties of magnetic field lines.
Answer:

1. Magnetic field start from north and end at south.
2. They never intersect each other.

PSEB 10th Class Science Important Questions Chapter 13 Magnetic Effects of Electric Current

Multiple Choice Questions:

Question 1. The direction of magnetic field produced on passing electric current in a conductor is determined by
(A) MaxweI1s Left hand rule
(B) Fleming’s right hand rult
(C) Fleming’s left hand rule
(D) Faraday’s law.
Answer:
(A) MaxweJi Left hand rule

Question 2. The direction of the force produced in a current carrying coil placed in a strong magnetic field is determined by
(A) Maxwell’s right hand rule
(B) Fleming’s right hand rule
(C) Fleming’s left hand rule
(D) Faraday’s law.
Answer:
(C) Fleming’s left hand rule

Question 3. What is the colour of neutral wire in a domestic electric circuit?
(A) Black
(B) Red
(C) Green
(D) No specific colour.
Answer:
(A) Black

Question 4. When a current carrying wire and neutral wire come in contact so that heavy current begins to flow, this arrangement is called:
(A) Overloading
(B) Short circuit
(C) Earthing
(D) All the above.
Answer:
(B) Short circuit

Question 5. Connecting metallic frame of high power electrical appliances with the earth wire of domestic circuit is called
(A) Overloading
(B) Short circuit
(C) Earthing
(D) Ail of these
Answer:
(C) Earthing

Question 6. Which of the following is source of direct current?
(A) Dry cell
(B) Button cell
(C) Lead battery
(D) All these.
Answer:
(D) All these.

Question 7. The device used for producing electric current is called a :
(A) Generator
(B) Galvanorneter
(C) Ammeter
(D) Motor.
Answer:
(A) Generator

Question 8. Similar magnetic poles
(A) Attract
(B) Repel
(C) Both attract and repel
(D) None of these.
Answer:
(B) Repel.

Question 9. Magnetic field lines are.
(A) Straight lines
(B) Curved
(C) Closed curves
(D) Triangular.
Answer:
(C) Closed curves

Very Short Answer Type Questions

Question 1. What is a dynamo?
Answer:
Dynamo. It is a device which converts mechanical energy into electric energy.

Question 2. On what principle is an a.c. motor based?
Answer:
It is based upon Fleming’s left hand rule.

Question 3. What is an electric motor?
Answer:
Electric motor. It is a device which converts electric energy into mechanical energy.

Question 4. List three sources of magnetic field?
Answer:
Electromagnet, load stone, solenoid, bar magnet.

Question 5. Name the physical quantity whose S.I. unit is weber/m2.
Answer:
Magnetic field.

Question 6. In which part of a bar magnet, the magnetic field lines are more denser?
Answer:
At the poles of a magnet.

Question 7. How does the strength of the magnetic field at the centre of a circular coil of a wire depend on : (a) radius of the coil (b) number of turns of the coil.
Answer:
(a) Strength of magnetic field (B) ∝ 1 / radius of the coil (r)
(b) Strength of magnetic field (B) ∝ Number of turns of the coil (N).

Question 8. Name any two devices which uses electric motor as an essential component in their working.
Answer:

1. Water pump
2. Electric fan.

Question 9. Define an electromagnet.
Answer:
Electromagnet. The combination of an soft iron core and current carrying insulated wire wound over it, is called an elctromagnet.

Question 10. Define magnetic pole.
Answer:
Magnetic poles are points near the ends of a magnet where magnetic field is maximum,

Question 11. Give a property of a Magnet.
Answer:
Directive Property (stays always in N-S directions, when suspended freely).

Question 12. Name two electric devices which act on magnetic effect of electric current.
Answer:

1. Electric bell
2. Loud-speaker.

Question 13. What is electric fuse?
Answer:
Fuse is a safety device which saves electric circuit from damage due to over loading a short circuit.

Question 14. Which electrical phenomenon is responsible for deflection of galvanometer needle in the given figure?

Answer:
Electric Induction.

Short Answer Type Questions

Question 1. How will you prove that current flowing through a copper wire produces magnetic effect?
Answer:

• On passing current through a thick copper wire with a magnetic needle placed in its neighbourhood will be deflected.
• This shows that current flowing through a copper wire produces magnetic field all round it.

Question 2. What do you understand by magnetic effect of current? To understand this effect give Oersted experiment.
Answer:
Magnetic Effect of Electric Current. When electric current flows through a conducting wire, then magnetic field is produced all round it. This effect of electric current is known as magnetic effect.

Oersted Experiment. Oersted took a conducting wire XY and placed a magnetic needle under this wire, then pressed the key and passed current through the wire in the direction from X to Y as shown in figure (a). He observed that the N-pole of the magnetic needle gets displaced towards west. Similarly, he repeated the experiment by reversing the direction of flow of current in the wire by changing the terminals of battery connected to the ends of the wire. This time the direction of deflection of the needle was opposite i.e. from Y to X as shown in figure (b).

The direction of deflection of magnetic needle can be remembered by ‘SNOW’ rule. This rule states that “If current in the wire XY flows from south pole to north pole when the current carrying conductor is placed above the conductor then the N-pole of the conductor gets displaced towards the west direction.”

Question 3. Define magnetic field and write important properties of magnetic lines of force.
Answer:
Magnetic Field. It is the field or region around a magnetic in which the effect of magnet (force of attraction or repulsion) can be experienced.
Magnetic Lines of Force. The path on which a unit N-pole moves when it is free to move, is called magnetic line of force.

Important properties of magnetic lines of Force.

• Outside the magnet, magnetic lines of force start from north pole (N-pole) of the magnet and end at its south pole (S-pole).
• No two magnetic lines of force intersect each other and if they do so then it would mean that the point of intersection there are two directions of magnetic lines of force which is impossible.
• At any point or the magnetic field the direction of the field lines is along the tangent at that point.

Question 4. How will you represent diagrammatically uniform and non-uniform magnetic field?
Answer:
The uniform magnetic field represented by equally spaced parallel lines while non-uniform magnetic field is represented either by non-parallel lines or by unequally spaced lines. These are shown in the diagrams below :

(i) Uniform magnetic field, (ii) and (iii) Non-uniform magnetic field.

Question 5. In the given figure what are the lines shown around the magnet called? Also give any two properties of these lines.

Answer:
In the figure the lines shown around the magnet are called magnetic field lines.

Properties of magnetic field lines,

• Outside magnetic: the magnetic field lines start from the N-pole of the magnet and end at the S-Pole while inside the magnet the direction of magnetic lines are from S-Pole to the N-Pole.
• The direction of magnetic field at any point of the magnetic line of force is represented by the tangent drawn to the curve at that point.

Question 6. What is Maxwell’s Right hand thumb Rule? For what purpose this rule is used?
Answer:
Maxwell’s Right Hand Thumb Rule According to this rule “To find the direction of magnetic field around a straight carrying conductor if the straight conductor is held in right hand in such a way that your thumb points in the direction of current then the curling fingers would determine. The direction of magnetic field lines.”

The rule is used to determine the direction of magnetic field lines produced around a straight conductor carrying current.

Question 7. Which rule is shown in the figure? Define the rule. In which device this rule is used?

Answer:
Fleming’s Left Hand Rule is shown in the figure.

Fleming’s Left Hand Rule. According to this rule, stretch your left hand in such a way that the thumb, forefinger and central finger are mutually at right angle to each other. If the fore finger points in the direction of the magnetic and the central finger points in the direction of current, the thumb gives the direction of the force acting on the conductor.

This rule is used in the working of an electric motor.

Question 8. Fleming’s left hand rule, Label the diagram.

Answer:
Fleming’s Left Hand Rule. According to this rule, stretch your left hand in such a way that the thumb, forefinger and central finger are mutually at right angle to each other. If the fore finger points in the direction of the magnetic and the central finger points in the direction of current, the thumb gives the direction of the force acting on the conductor.

This rule is used in the working of an electric motor.

1. Force acting on the conductor OR direction of motion
2. Direction of magnetic field
3. Direction of current

Question 9. Name the law shown in the figure. Label 1 and 2 law.

Answer:
The figure represents Fleming’s Right Hand Thumb Rule

1. Magnetic Field
2. Current induced in the conductor.

Question 10. In the alongside figure a straight conductor B is carrying current in the vertical downward direction.
(a) What will be the direction of magnetic field lines around the conductor?
(b) Name the law which you have used for your answer.

Answer:
(a) Clockwise.
(b) Maxwell’s Righthand Thumb Rule.

Question 11. What is Electro-magnetic Induction?
Answer:
Electro-magnetic Induction. The process of producing e.m.f by changing the magnetic lines of force linked with the circuit, is called electromagnetic induction. The electromagnetic force (e.m.f) so produced is called induced electromotive force.

Question 12. List some such electric appliances in which electric motor is used.
Answer:
With the help of electric motor all such appliance work in which it is required to produce rotatory in motion e.g. Electric fan, tape recorder, mixer etc.

Question 13. What is Electric Fuse? What is its importance?
Answer:
Electric Fuse. It is a device used in electric circuits which prevents the other electric appliances connected in the circuit from being damaged by high current. It has low meeting point.

Importance (use) of Electric Fuse. If for some reason heavy current begins to flow in the circuit then fuse wire melts and breaks the circuit and accident is prevented.

Question 14. Why the fuse wire should have high resistance and low melting point?
Answer:
The fuse wire should have high resistance and low melting point because when it is connected in series then heavy current will not flow through fuse wire due to its high resistance and the heat produced will melt it due to its low melting point. Thus the electric appliances connected in the circuit would be saved from damage.

Question 15. What is meant by over-loading?
Answer:
Over-loading. Overloading means to draw large current from the mains. This happens when many appliances are connected with single socket simultaneously. The supply wires as well the wires used in household wiring has a specific rating. The rating of 15 A means that if a current upto 15A is passed through the circuit, there is no likely damage feared to the circuit. But if a current more than maximum allowed limit is passed, there may be excessive heating of the wires and it may damage the wiring.

Question 16. When does an electric short-circuit occur?
Answer:
Short-circuiting. An electric circuit is said to be short-circuited if a live wire touches neutral wire or earth wire, a large current flows through the circuit due to almost zero resistance of the circuit. This results in increase of temperature and hence heating of wires which may cause fire or damaging the appliance.

To save the circuit from damage due to over-loading or short-circuiting, a fuse of proper rating is put in each circuit.

Question 17. What are hazards of electricity?
Answer:
Hazards of Electricity. Electricity is the most important source of energy. A proper use of electricity is a boon while improper use is very dangerous and may prove to be fatal. There are number of hazards.

• If by accident a person touches a live wire, he gets a very severe shock which may prove fatal.
• Loose connections, defective switches and sockets can cause sparking which may lead to fire.
• Short circuiting due to damaged wires or overloading of circuits can cause fires.

Long Answer Type Questions

Question 1. Give magnetic field due to solenoid. On what factors the strength of the field depends?
                                     Or
What is solenoid? How does a solenoid behave like a bar magnet?
Answer:
Solenoid. A solenoid is a long circular coil containing a large number of close turns of insulated copper wire.
Magnetic field due to solenoid. When an electric current is passed through the solenoid, it produces magnetic field around it as shown in Figure. Magnetic field produced by a current carrying solenoid is similar to the magnetic field produced by a bar magnet. The magnetic lines enter from one end of the solenoid and leave at the other end. If we look from left end, the current appears to be passing in the solenoid in clockwise direction and hence it acts as a south pole according to clock rule. If the solenoid is viewed from right side, the current appears to be in anticlockwise direction. Hence, right hand side face of the solenoid behaves as if this were a north pole.

Magnetic field due to current carrying solenoid is similar to bar magner.

Since the current flows in the various turns of the solenoid in the same direction, the magnetic field produced by each turn of the solenoid adds up, giving a very strong resultant field inside the solenoid.
Hence, a solenoid may be used in making electromagnets.

The strength of the magnetic field produced depends upon the following three factors :

1. Number of turns. The more the number of turns, the stronger will be the magnetic field produced.
2. Strength of the current in the solenoid. Larger the current, stronger will be the magnetic field produced.
3. Nature of core of solenoid. The strength of the field depends upon the core on which the coil is wound. For air core, field is very weak whereas for soft iron-core, the field is very strong. .

Question 2. What is an electromagnet? Upon what factors its strength depends?
Answer:
Electromagnet: The combination of soft iron core and a current carrying insulated copper wire wound over it is called an electromagnet.
Very strong electromagnets can be produced by winding an insulated copper wire on a soft iron core.
When current is passed through a solenoid, a magnetic field is produced. Now if a soft iron core is placed inside the solenoid, the strength of the magnetic field becomes very large. The reason for increase in magnetic field is due to the fact that iron gets magnetised by induction.

Electromagnet

A simple electromagnet is as shown in Figure. To make an electromagnet, a soft iron core is placed inside a solenoid having large turns of insulated copper wire. The two ends of the solenoid are connected to a battery and a key.

Electromagnet lifting a car.

Strength of electromagnet depends upon

• Number of turns. Strength of electromagnets is directly proportional to the number of turns.
• Current flowing. More the current flowing through the wire, stronger is the electromagnet.
• Length of the air gap. Lesser the length of air gap between poles, stronger is the electromagnet.
• Air gap between the poles of a U-shaped electromagnet is small, hence it is very strong

Question 3. Explain principal, construction and working of D.C. generator.
Answer:
Electric Generator. It is a device that converts mechanical energy into electric energy. It only converts the form of energy into another form. In generator, mechanical energy is the input while electric energy is obtained as output.

Principle: Generator is based on the principal that “when a conductor cuts magnetic lines of force, then according to the Faraday’s, electromagnetic law, electromagnetic force (emf) is induced in it which makes induced current to flow in the circuit when the circuit is closed”.

Construction: A D.C generator has the following main parts :

• Armature: It consists of a coil ABCD in which an insulated copper wire is wound into number of turns around a soft iron core, called armature. It is fixed on an axis and is capable to rotate with steam or running water.
• Field Magnet: There are two strong pole pieces (electro magnet)-in which the coil is placed forms a field magnet. In small generators, permanent magnets while in big generators electromagnets are used.
• Slip Rings: At the ends of the coil two slip rings R₁, and R₂ are attached. These two work as commutators.
• Carbon Brush Split: Rings R₁ and R₂ soft touch against the carbon brushes B₁ and B₂. When the coil rotates the slip rings R₁ and R₂ in turn touch B₁ and B₂.
• From carbon brushes B₁ and B₂ electric current is taken to the load (output). In the diagram galvanometer is shown in place of load.

Working. When the coil rotated about its axis, then emf is induced in arms AB and CD of the coil. The direction of induced electromagnetic force can be determined by Fleming’s right hand rule.

Suppose in the beginning the coil is in vertical position with its arm AB in the lower position and CD in the upper position. When the coil is rotated about its axis then during the first half rotations the arm AB moves in the upward direction and CD in the downward direction. According to Fleming’s right hand rule the direction of induced current in arm AB will be from A to B and in CD it is from C to D.

The arm AB on reaching the upper most position begins to move downward while the arm CD would begin to move in the upward direction. Therefore, the direction of induced current in the arms AB and CD gets reversed but to keep the direction of current in the load (output) same, the split rings are used. In the second half of the rotation the end of the coil comes in contact with the split ring R2 and the end D touches the split ring Rx so that the direction of current remain same in the load.

Question 4. Arrange an activity to show that current is produced due to change in magnetic field.
Answer:
Make a coil XY having large number of terms of insulated copper wire wound area as shown in the figure. Connect the ends of the coil to a sensitive galvanometer.

Now quickly bring N-pole of a bar magnet but see that it does not touch the coil. You will see deflection in the galvanometer which proves that current is flowing in the galvanometer. Note the direction of deflection in the galvanometer.

Now take away the magnet as shown in fig 13.20. Again you will notice deflection in the galvanometer but diis time the direction of deflection is opposite to the first. If we do not move the magnet and keep it stationary near the coil then there is no deflection in galvanometer. This experiment shows that when there is a relative motion between the coil and the magnet then current is induced in the circuit.

Question 5. What are essential precautions to be used while using electricity?
Answer:
The following precautions should be observed while using electricity :

• Turn off all switches including main switch whenever sparking or fire is noticed.
• All connections must be tight. Wires must be covered with proper insulation of proper thickness. All joints must be covered with insulating tape of a good quality. Defective / switches should be immediately replaced.
• Fuses should always be connected to live wire. The earth wire must be connected to the body of electric appliance.
• Fuse must be of proper rating and should always be connected to live wire.
• Whenever repairs are needed, switch off main switch. If however , repairs need a direct handling of live wire, rubber gloves, rubber shoes and a plier with insulated handle should be used.
• If inspite of all the precautions, a person gets a shock due to accidental touching a live wire, one should try to provide such a person with support of some non-conducting material like wood, plastic or rubber. Never try to pull away person by your hand.
• Always put on dry rubber shoes while repairing the circuit.

Question 6. What are magnetic field lines? How can the magnetic lines of force due to a bar magnetic be shown?
Answer:
Magnetic Field. The area of field around the magnet in which the force of attraction or repulsion due to magnet is experienced, is called Magnetic field.

Magnetic field lines: It is the path in the magnetic field, along which the unit N-pole would move when it is free to move.
magnet can be shown by the following two methods :
1. Place a magnet on a cardboard sheet. Now spread iron filings on the Cardboard and tap it gently will when the iron filings will arranged itself in the pattern of magnetic lines of force.

2. Drawing magnetic lines of a bar magnet Activity. Place a bar magnet on a white sheet and mark its boundary with pencil. Place a magnetic compass needle near the North-pole of the magnet. Now mark the position of poles of the magnetic needle with a sharp pencil. Now move the magnetic compass needle in such a position so that its S-pole is in the position of previous position of North-pole, Again mark position of N-pole with pencil. Repeat this process so that you reach south- pole of the bar magnet. Now join these marked points making a free hand curve.

This curve represents a magnetic line of force. In the same way by taking another point near the north pole of the bar magnet get different line of force. By taking various points and drawing different curve for each of the points you will get a pattern of magnetic lines of force due to a bar magnet.

Magnetic lines o force around a bar magnet.

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